Machine tools generally hold a work piece at one end with a chuck. Often, the other end of the work piece will be supported, steadied or otherwise contacted by a live or dead center. A dead center is a device that contacts a work piece without rotating. A live center is a device that contacts a work piece and the portion of the center that contacts the work piece rotates along with the work piece.
The portion of the live center that rotates along with the work piece is known as a spindle. The spindle is mounted within a housing where the housing of the live center generally does not rotate. Bearings are used to support and facilitate the rotation of the spindle within the housing. Often, it is desirable to provide lubrication for the bearings. In instances where lubrication is used, oil can leak out of the live center or seep along the spindle thus depriving the bearings of lubrication.
Accordingly, it is desirable to provide a method and apparatus that substantially seals the oil within the live center so that the oil can provide lubrication for the bearings.
Live centers are also hampered by other problems. For example, modern manufacturing techniques include using heavy amounts of coolant, also referred to as cutting fluid, when working on a work piece in a machine tool. The work piece may be constantly subjected to a high-pressure stream or streams of fluid which provide several functions. Among the functions performed are that the coolant keeps the work piece and cutting tool cool, and removes chips and other unwanted material from the area being cut by the cutting tool.
The cutting fluid may have in suspension chips or material of the work piece that has been removed by the cutting process. Should some of this fluid and its accompanying material enter the live center, it could potentially interfere with the rotation of the spindle within the live center. For example, chips could jam between the spindle and some other portion of the live center such as the bearings. Also, the chips or material can damage the bearings and bearing races preventing them from operating efficiently or, in the extreme case, jam the spindle from rotating. Alternatively, cutting fluids usually degrade the effectiveness of the lubricant used in the bearings, again creating a variety of problems.
Accordingly, it is desirable to provide a method and apparatus which substantially seals the interior of the live center from contaminants such as cutting fluid, chips and other unwanted material from entering the live center.